Board Thread:Pokémon Help/@comment-32216993-20170607144951/@comment-27535813-20170609101447

You can click here(this can be found in the wiki), to know more about the evolutionary stones.

According to the appendix you can find it at: Lagoona Trenches in Lagoona Lake(after the 2nd gym) or the Stone Shop in Anthian City(which is the 4th gym area). Raichu is decent at best for story purposes I suppose.